std::vector for parent and child class

Question

I need to create a vector that can contain my parent class and sub class data.

This is what i do..

Vehicle is the parent class

Car is the child class

About Car.cpp , it got the following

struct Point
{
    int x,y
};

class Car : public Vehicle
{
private:
    Point wheelPoint[4];
    double area;

public:
    void setPoint();
};

void Car::setPoint()
{
    int xData,yData;

    cout << "Please enter X:";
    cin >> xData;

    cout << "Please enter Y:";
    cin >> yData;

    wheelPoint[i].x = xData;
    wheelPoint[i].y = yData;
}

Then at my main.cpp

At my main.cpp

vector<VehicleTwoD> list;
VehicleTwoD *vehicle;
Car *car = new Car;
string vehicleName;

cout << "Please input name of vehicle";
cin >> vehicleName;

vehicle = new Car;
car->setPoint();

list.push_back( Vehicle() );
list.back().setName(vehicleName);

Here the issues.. how i put my wheelPoint of car into this vector also.

What i want to achieve is a vector that can contain

Vehicle Name: Vehicle Name (private variable at Vehicle - Parent Class)
Wheel Point[0]: Point (X,Y) ( private var at Car - Child Class)
Wheel Point[1]: Point (X,Y) ( private var at Car - Child Class)
Wheel Point[2]: Point (X,Y) ( private var at Car - Child Class)
Wheel Point[3]: Point (X,Y) ( private var at Car - Child Class)

What is `Vechicle2D`? The way to create vector that can contain both your parent class and your child class is to have a vector of *pointers* to your parent class, and to use *virtual functions*, `vector` in other words. — john, Oct 26 '12 at 17:09

score 12 · Accepted Answer · answered Oct 26 '12 at 17:08

12

Containers of objects suffer from object slicing. You'll need a vector of pointers (preferably smart):

vector<std::unique_ptr<Vechicle>> vehicleVector;

to which you can do:

vehicleVector.push_back(new Vehicle);
vehicleVector.push_back(new Car);

Having a vector of objects will cut off all type information that is beyond Vechicle - so, a Car will be turned into a Vehicle, losing all additional information.

answered Oct 26 '12 at 17:08

Luchian Grigore

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The OP seems to be confused about how polymorphism works, based on how he does `list.push_back( Vehicle() );` and `list.back().setName(vehicleName);` instead of `car->setName(vehicleName);` and `list.push_back(car);`. – Geoff Montee Oct 26 '12 at 17:11
1

doesnt really work for me.. i try to push_back new Car but it dont seems to work – user1777711 Oct 26 '12 at 17:13
1

@user1777711 Well that's because you are doing it wrong. But without *real code* it's hard to know why. – john Oct 26 '12 at 17:15
@user1777711 did you change the declaration of the vector? – Luchian Grigore Oct 26 '12 at 17:16
1

@user1777711 did you `#include `? – Luchian Grigore Oct 26 '12 at 17:23

score 3 · Answer 2 · answered Sep 27 '17 at 15:13

I had this same problem and I fixed it by first using and then compiling using c++14. 11 will work as well but I wanted to use some of 14's new features so I did that. I hope this helps!

#include <memory>

std::vector<std::unique_ptr<sf::Shape>> _shapes;

std::vector for parent and child class

2 Answers2

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